I. Technical Field
The present invention relates to an interdigital capacitor and to a method of producing an interdigital capacitor and, more particularly, to an interdigital capacitor having fingers alternately connected to a center line of a coplanar waveguide and a method for making the interdigital capacitor.
II. Related Art
Interdigital capacitors are used in monolithically intergrated microwave circuits (MMIC) as blocking capacitors or as low radiation, or emission, capacitors in filter structures and resonant circuits. Interdigital capacitors are known passive components for MMIC. See for example, J. Frey, Microwave Integrated Circuits, Artech House, Inc., 1975, page 351.
To optain capacitively loaded coplanar lines for MMICs for ultrahigh frequency and direct current networks, it is customary to use MIM (metal-insulator-metal) capacitors. See for example, Goyal, Monolithic Integrated Circuit Design, Artech House, 1989. Current supply for active components of MMICs in such a realization is effected by using a separate, high-ohmic stub line having a galvanically reinforced center line. To form the dielectric medium of the MIM capacitor, additional process steps are necessary during the MMIC manufacturing process. Moreover, problems arise with respect to the breakthrough voltage of the dielectric medium. Further, in order to avoid undesirable couplings when using MIM capacitors, a relatively large space must exist between the metal faces of the capacitor and critical conductor path structures. This has a detrimental effect on packing density and, consequently, on manufacturing costs of MMICs.